Method and apparatus for process control in time division multiplexed (TDM) etch process

Abstract

The present invention provides a method for controlling pressure in a vacuum chamber during a time division multiplexed process. A throttle valve is pre-positioned and held for a predetermined period of time. A process gas is introduced into the vacuum chamber during the associated plasma step (deposition or etching) of the silicon wafer. At the end of the predetermined period of time, the process gas continues to flow with the throttle valve being released from the set position. At this point, the throttle valve is regulated through a proportional derivative and integral control for a period that lasts the remaining time of the associated plasma step.

Description

CROSS REFERENCES TO RELATED APPLICATIONS[0001]This application claims priority from and is related to commonly owned U.S. Provisional Patent Application Ser. No. 60 / 460,932, filed Apr. 7, 2003, entitled: A Method and Apparatus for Process Control in Time Division Multiplexed (TDM) Etch Processes, this Provisional Patent Application incorporated by reference herein.FIELD OF THE INVENTION[0002]The present invention generally relates to the field of semiconductor wafer processing. More particularly, the present invention is directed to a method and apparatus for controlling the reaction chamber pressure during a time division multiplexed etching and deposition process.BACKGROUND OF THE INVENTION[0003]The fabrication of high aspect ratio features in silicon is used extensively in the manufacture of micro-electro-mechanical (MEMS) devices. Such features frequently have depths ranging from tens to hundreds of micrometers. To ensure manufacturability, the etching processes must operate at ...

AI Technical Summary

Benefits of technology

[0026]A feature of the present invention is to provide a method for anisotropically etching a feature in a substrate. The method comprising the following steps. The substrate is placed within a plasma chamber and subjected to an alternating cyclical process having an etching step and a deposition step. The pressure of the plasma chamber is regulated by setting a throttle valve at a predetermined position set point for a predetermined period of time to ensure that the chamber pressure does not overshoot or undershoot the desired operating level while minimizing the time required to reach the set point value. A first process gas, such as octofluorocyclobutane, is introduced into the plasma chamber for depositing a film onto the substrate during the deposition step of the alternating cyclical process. A plasma is ignited for a recipe period of time for the deposition step of the alternating cyclical process. A closed loop pressure control algorithm is enabled after the predetermined period of time expires. Then, the pressure of the plasma chamber is controlled at a recipe specified pressure set point through a closed loop pressure control for the remaining time of the deposition step. Next, the pressure of the plasma chamber is again regulated by setting the throttle valve at a predetermined position set point for a predetermined period of time to ensure that the chamber pressure does not overshoot or undershoot the desired operating level while minimizing the time required to reach the set point value. A second process gas, such as sulfur hexafluoride is introduced into the plasma chamber for etching the substrate during the etching step of the alternating cyclical process. A plasma is ignited for a recipe period of time for the etching step of the alternating cyclical process. A closed loop pressure control algorithm is enabled after the predetermined period of time expires. Then, the pressure of the plasma chamber is controlled at a recipe specified pressure set point through a closed loop pressure control for the remaining time of the etching step.

[0031]The predetermined position set point can be adjusted by an offset from about 0.5 to 2 of the throttle valve position of the preceding like step of the alternating cyclical process. The predetermined position set point can change using a predefined function for the duration of the predetermined period of time. The predetermined position set point can be modified based on pressure performance of a preceding like step of the alternating cyclical process such as minimizing the time to reach the recipe specified pressure set point or minimizing the deviation from the recipe specified pressure set point.

[0032]The predetermined period of time is about 0.05 to 0.5 seconds long. The predetermined period of time can be modified based on pressure performance of a preceding like step of the alternating cyclical process such as minimizing the time to reach the recipe specified pressure set point or minimizing the deviation from the recipe specified pressure set point.

[0033]Yet another feature of the present invention is to provide a method of pressure control in a time division multiplex process. The method comprising the following steps. The process pressure in a vacuum chamber is regulated in at least one step of the time division multiplex process by setting a throttle valve at a predetermined position set point for a predetermined period of time to ensure that the chamber pressure does not overshoot or undershoot the desired operating level while minimizing the time required to reach the set point value. At least one process gas is introduced into the vacuum chamber for processing a substrate according to the time division multiplex process. A closed loop pressure control algorithm is enabled after the predetermined period of time expires. Then, the pressure of the vacuum chamber is controlled at a recipe specified pressure set point through a closed loop pressure control for a period that lasts the remaining time of the processing step of the time division multiplex process.

Problems solved by technology

However, as described earlier, the inability to control pressure during the transition of the constantly alternating TDM process steps is the real issue, and cannot be addressed by Kessel's technique.

Additionally, many TDM processes employ alternating process steps which last only a few seconds or shorter, which makes pressure control impractical using the disclosed technique.

However, in many TDM processes, changing process gas flow rate during a process step is undesirable.

Beyer does not teach how to use this technique in TDM processes.

While Puech teaches the control of pressure in the TDM processes that employ process steps on the order of one second, the method does not teach the use of actively regulating throttle valve in pressure control.

The current methods of pressure control for TDM processes, Pressure Control and Position Control, have limitations.

One problem with pressure control mode in a TDM process is that, in practice, there is typically a trade off between achieving fast pressure response time while minimizing set point deviations.

A problem with the current method of Position Control mode in a TDM process is unacceptably long pressure response times. While position mode minimizes process overshoot, the slower response times result in the chamber pressure spending a large fraction of the process time approaching the requested set point value (i.e., out of compliance with the recipe specified set point).

Another problem with the position control mode method is that it is an open loop pressure control algorithm.

Therefore, there is not any correction for perturbations in gas flow or pumping efficiency.

These perturbations tend to cause the process pressure, and subsequent process performance, to vary with time.

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